When high concentrations of an acidic component, such as CO2, H2S, HF, HCl, H2SO4, or H3NO3, are present in a gas, the gas is generally referred to as an “acid gas.” The acidic component of acid gas will generally cause the pH of liquids contained in the gas, such as water, to fall to between about 3 and 5, for example. In gas compression technology, liquids (e.g., water) with a pH below 4 have been shown to cause Sulfide Stress Cracking (SSC), a form of corrosion, in the metal or alloy components of the gas compression equipment. Typically, corrosion is the most severe during the initial stages of compression, or after an inter-cooler, where the gas temperature is lowered and condensate is formed, but is not completely removed from the gas.
Gases are often cooled before compression and between stages of compression to improve the efficiency of compression, and to keep the gas temperature low enough to be handled with common materials of construction. Process gases are often cooled by water or air-cooled heat exchangers to lower their temperature to near ambient, or at least below about 120° F. If the gas has water vapor in it, the cooling of the gas below the dew point results in the condensation of water from the gas. The dew point is the temperature and pressure at which water vapor condenses from the gas phase to the liquid phase.
Conventional compressor systems may include one or more dehydration systems configured to remove moisture from a process gas before it enters a compressor. A dehydration system may include a glycol system that is capable of removing all free moisture and all but about 10 ppm of water (or less). However, such glycol systems may be expensive, because the component parts must be made of highly expensive alloys that can tolerate corrosive conditions.
More commonly, a conventional compressor system may include an cooling unit configured to cool a process gas to produce condensate, and then pass the cooled gas containing the condensate to a demister configured to remove condensate from the cooled process gas. However, demisters are known to be incapable of removing all condensate from a process gas. The extent to which condensate is removed varies with the design of the heat exchanger and the demister. Thus, an cooling unit/demister configuration may, at best, leave the process gas saturated with water, and depending on the efficiency of the demister, an cooling unit/demister configuration could even leave condensate in the process gas.
Thus, there is a need for a more effective and less expensive system and/or method for reducing corrosion in turbomachines by reducing or eliminating liquid water from process gas.